Electron multiplier



April 15, 1941.

w. FLECHSIG ELECTRON MULTIPLIER Filed April 21, 1938 HH-HH HHHH I H IH IH HI HU I.

HHHHH H -NH nu ll" H I Patented Apr. 15, 1941 Werner Flechsig, Berlin-Charlottenburg,

Ger-

many, assignor to the firm Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application April 21, 1938, Serial No. 203,418 In Germany April 23, 1937 4 Claims.

This invention relates to electron multipliers operating by secondary emission, and more particularly to such multipliers in which an electron stream successively impacts secondarily emissive electrodes supplied with increasing positive potentials.

In order to obtain good efficiency in such devices, it is necessary to sensitize the impacted electrodes in order to obtain a large gain of secondary electrons upon impact. Difficulties arise if it is desired to multiply the electron stream to such an extent that currents of the order of between 30 and 100 milliamperes are obtained at the output electrode, because currents of such magnitude naturally cause heating of the sensitized electrodes, which leads to destruction of the sensitive layer. While normal discharge tubes can be operated in such a manner that the electrodes begin to show a bright glow, at which no considerable evaporation takes place, secondaryemitting surfaces prepared with caesium endure only much lower temperatures of the order of 100 centigrade.

It is the object of the invention to overcome the above-mentioned defects and to provide an electron multiplier in which high output currents can be obtained without excessive heating and without the necessity of maintaining low output capacitance.

In the following, an embodiment of the invention shall be described in which the advantages of the invention are incorporated.

Figs. 1 and 2 show such embodiments.

The final stages of the multiplier are so arranged that a perforated collecting electrode is interspersed between the last secondary-emitting electrode (which is solid) and the last but one secondary-emitting electrode (which is perforated). The preceding electrodes may have the shapes of meshworks, or any shape as may seem desirable. In this arrangement in which the collecting electrode is surrounded by electrodes on both sides, it possesses a greater capacitance to ground than the last secondary-emitting electrode, which is at the end of the discharge space and may, therefore, radiate heat particularly well.

In Fig. 1 a photocathode I is located at one end of the vacuum receptacle. The photoemission is multiplied by a plurality of grids 2. The electron stream passes through the perforated collecting electrode 3, impacts solid electrode 4 and returns to collecting electrode 3. The potentials of the electrodes increase in the direction toward the collecting electrode. Electrode 4 possesses the direction of the electron stream, which possess good heat'conductivity but poor heat radiation.

In some cases, it may seem preferable to increase the width of the strips or wires from the center toward the periphery of the collecting electrode.

' Cooling fins 5, which may be distributed in the shape of a star around the periphery of collecting electrode 3, may consist of a good heat conductor which may be provided with a suitable surface (such as, for instance, metallic oxide) in order to obtain good heat radiation.

Fig, 2 shows another embodiment. The drawing shows only the final stages in the tube. The collecting electrode is shown at 3, and the last secondary-emitting stage at 4. The collecting electrode in this case fills the entire cross-section of the tube, and is connected to a metallic portion 6 of the vacuum receptacle. This connection is so made as to grant good heat conductivity. Metallic portion 6 is fused to glass portions '1 and 8 in the well-known manner, and may consist of copper or an alloy of chromium and iron. In this case the heat produced at the collecting electrode canunimpededly be radiated into the surrounding space exterior to the vacuum receptacle. In order to obtain very efficient cooling, it may be preferred to provide a circular container around the metallic portion of the vacuum receptacle, and to provide a flow of water through space 9.

A well-cooled anode makes all considerations with respect to the voltage between collecting electrode and previous multiplying stages unnecssary. This voltage can readily be made sufiiciently high to guarantee complete saturation.

I claim:

1. An electron tube comprising an electron source, a plurality of secondarily-emissive electrodes and a perforated collecting electrode interspersed between two of said secondarily-emissive electrodes, said collecting electrode being providedwith liquid cooling means for conveying substantially all heat into space apart from said secondarily-enfissive electrodes.

2.. An electron multiplier device comprising an envelope, a plurality of electrodes therein, said electrodes including a secondary-emissive electrode and an electron permeable collector electrode for receiving electrons emitted from said secondary-emissive electrode, said collector elecnext higher, and collecting anode 3 the highest trode only having a portion thereof in direct con-.-

tact with a liquid cooling medium external of said envelope.

3. An electron multiplier device comprising an envelope of insulating material including a section of conductive material, and a plurality of electrodes in said envelope including a secondaryemissive electrode and an electron permeable collector electrode for receiving electrons emitted from said secondary-emissive electrode only, said 4. An electronmultiplier device comprising an envelope of insulating material including a metallic section having a channel for the flow of a liquid cooling medium, and a plurality of electrodes in saidoenvelope including a secondaryemissive electrode and an electron permeable collector electrode for receiving electrons emitted from said secondary-emissive electrode, said collector electrode only making contact with said collector electrode making contact with the con- 0 channeled section of said envelope.

ductive section of said envelope.

WERNER FLECHSIG. 

